Method for blow molding plastic articles

ABSTRACT

A METHOD OF BLOW MOLDING A HOLLOW ARTCLE WHEREIN THE PARISON IS PREBLOWN AND THEN ALLOWED TO PARTIALLY DEFLATE AND SHRINK IN SIZE TO OBTAIN THE BENFIT OF STRETCHING DURING PRE-INFLATION WHILE AVOIDING CHILL MARKS IN THE FINISHED ARTICLE.

May 18, 1971 H. SHAW ETAL 3,579,622

METHOD FOR BLOW MOLDING PLASTIC ARTICLES Original Filed Oct. 17, 1966 4Sheets-Sheet 1 7? INVENTOR.

CHARLES H. SHAW BY ROBERT s. STRAUSS ATTORNEY1% a a 7%; MMw .13 :E a \Na V. w 7 Z May 18, 1971 c. H. SHAW ETAL 3,579,622

METHOD FOR BLOW MOLDING PLASTIC ARTICLES Original Filed Oct. 17, 1966 4Sheets$heet a FIG. 3 '72 "/Ia. /X6

[NVEN'IOR CHARLES H. SHAW ROBERT G. STRAUSS ATTORNEY:

y 18, 1971 c. H. SHAW ETAL 3,579,622

METHOD FOR BLOW MOLDING PLASTIC ARTICLES Original Filed Oct. 17, 1966 4Sheets-Sheet 3 FIG. 5

FIG. 6

INVENTOR. CHARLES H. SHAW ROBERT G. STRAUSS ATTORNEY May 18, 1971 c.H.SHAW ETAL METHOD FOR BLOW MOLDING PLASTIC ARTICLES 4 Sheets-Sheet 4Original Filed Oct. 17, 1966 INVENTOR. CHARLES H. SHAW ROBERT e. STRAUSSBY 2 g ATTORNE Y United States Patent 3,579,622 METHOD FOR BLOW MOLDINGPLASTIC ARTICLES Charles H. Shaw, Bloomfield, and Robert G. Strauss,West Hartford, Conn., assignors to Monsanto Company, St. Louis, Mo.

Original application Oct. 17, 1966, Ser. No. 587,255, now Patent No.3,509,596, dated May 5, 1970. Divided and this application Apr. 10,1969, Ser. No. 839,746

Int. Cl. B29c 17/07 US. Cl. 264-99 1 Claim ABSTRACT OF THE DISCLOSURE Amethod of blow molding a hollow article wherein the parison is preblownand then allowed to partially defiate and shrink in size to obtain thebenefit of stretching during pre-infiation while avoiding chill marks inthe finished article.

This is a division of copending application Ser. No. 587,255, filed Oct.17, 1966. now US. Pat. No. 3,509,596, issued May 5, 1970.

This invention relates to improvements in an apparatus and process forforming plastic articles, and more particularly to an improved methodfor blow molding plastic articles.

In blow molding articles, for example bottles, by expanding a heatedtube or parison of thermoplastic material against the walls of a hollowmold, chilling and setting of the plastic occurs almost instantaneouslyon contact of the plastic with the walls of the mold cavity. When thissetting of the plastic occurs, no further expansion is possible, so thatthe parts of the body of the bottle first contacting the mold walls aregenerally of greater wall thickness than those parts formed by latercontact with the walls. It has been particularly difiicult in the past,therefore, to blow mold non-cylindrical or irregularly shaped bottleswith a uniform wall thickness wherein certain sections of the parisonmust be expanded further than other portions which may have alreadycontacted the mold walls. Uneven wall thickness results in poor impactstrength causing the bottles to break or buckle in the thinner sectionswhen top loaded, e.g., when stacked.

The difiiculty has been especially pronounced in blow molding the morerecently developed handleware bottles wherein a hand hole radiallyoffset from the axis of the bottle is provided by expanding the parisonaround cooperating protrusions extending from the walls of each moldhalf. These cooperating protrusions matingly contact when the mold isclosed and represent the mold configuration which yields the hand holein the finished article. To produce such a bottle it has been necessaryto position the parison asymetrically within the closed mold so that thepart of the parison which ultimately forms the body of the bottleadjacent the hand hole is located quite close to the corresponding wallof the mold cavity, while that part which will form the opposite side islocated considerably further away from its confining cavity wall andmust be expanded over a greater distance. On expansion, non-uniform wallthickness results, with the amount of plastic material in the area ofthe hollow handle and adjacent wall being greater than that in thediametrically opposite wall due to the difference in the amount ofexpansion which each side of the parison has undergone. To overcome thisvariability, extremely large diameter parisons requiring minimumexpansion have been used, but this approach results in excessive wastein the tail pinch area, is uneconomical, unnecessarily increases theweight of the plastic in the container, and requires larger 3,579,622Patented May 18, 1971 extrusion tooling (i.e., mandrels, dies) toproduce the larger diameter parison.

Accordingly it is the principle object of the present invention toprovide a method for producing hollow plastic articles havingnon-cylindrical cross sections with improved wall thicknessdistribution.

It is a particular object of this invention to provide a method foreconomically forming hollow plastic articles having non-cylindricalcross sections with improved wall thickness distribution while avoidingexcessive plastic consumption in formation of the article.

It is a further object of the present invention to provide a method forforming hollow articles of non-cylindrical cross section by modifyingthe shape of a normally tubular blank from which the article is formed,to a configuration more nearly conforming to that of the finishedarticle.

It is a further object of this invention to provide a process forforming hollow plastic articles having noncylindrical cross sectionswherein the amount of tail pinch is reduced.

It is an additional object of this invention to provide a process forforming hollow plastic handle type bottles.

It is a further object of this invention to provide a process forforming hollow plastic articles which allows the use of smallerextrusion tooling.

It is a still further object of the present invention to provide amethod to carry out the above objects.

Other objects of this invention will in part be obvious and will in partappear hereinafter.

These and other objects are accomplished by providing a method forforming hollow plastic articles having neck and body portions,comprising the steps of extruding moldable plastic material from asupply source downwardly through an outlet orifice to form a generallytubular length of the material, clamping the tubular length below theoutlet orifice to form a seal across the tubular length, injecting gasinto the portion of the length above the seal to partially expand saidportion, enclosing the partially expanded shape within a partible moldhaving adjacent neck and body forming cavities, and further expandingthe partially expanded shape to form the hollow article.

In describing the overall invention, reference will be made to preferredembodiments illustrated in the accompanying drawings, in which:

FIG. 1 is a partial, schematic, vertical, sectional view illustratingthe preferred apparatus embodiment at an early stage in the presentinventive process with the preinflation gas on;

FIG. 2 is a partial, schematic, vertical, sectional view illustratingthe parison cutting and sealing step of the process;

FIG. 3 is a schematic vertical sectional view illustrating the expandedparison and blowhead assembly;

FIG. 4 is a plan view illustrating the complete parison cutting andsealing assembly;

FIG. 5 is a side, elevational view of an alternate embodiment of thepresent invention illustrating parison gripping apparatus;

FIG. 6 is a plan view taken along the line 6-6 of FIG. 5;

FIG. 7 is a partial, schematic, vertical, sectional view illustrating amodified form of the present invention from that depicted in FIGS. 1 and2;

FIG. 8 is a partial, schematic, vertical, sectional view illustratingthe cut parison of the modified form of the present invention depictedin FIG. 7;

FIG. 9 is a partial, schematic, vertical, sectional view illustratingthe parison sealing step of the modified form of the invention depictedin FIG. 7.

With reference to the drawings wherein identical numerals refer toidentical parts, there is shown in FIG. 1 a generally vertical extrusionhead 12 having one side attached to an end of horizontal conduit 10,which in turn may have its other end connected to the discharge of aconventional worm extruder, not shown. Extrusion head 12 has acylindrical exterior wall 13, and a generally cylindrical verticallyextending reservoir 15 communicating with opening 11 in horizontalconduit 10. Cylindrical inner core or mandrel 22 is mounted withinreservoir 15 so as to define an annular cavity. At the lower end of theillustrated inner core 22, there is mounted an extrusion tip 23 whichprovides an inner surface of a parison defining outlet through which aheated and suitably homogenized organic plastic resin such as, forexample, polyethylene is extruded in generally tubular form. Extrusionring 26 is provided at the lower end of the extrusion head 12 havingcurved shoulder 27 which cooperates with generally convex downwardsurface 24 of extrusion tip 23 so as to define an annular outlet orifice14 in axial alignment with tip 23. Inner core 22 is bored to providepassageway 28 therein. Gas pressure supply conduit 30 has its oppositeends connected with passageway 28 and with a suitable low pressure gassupply source (not shown). The communication may be continuallymaintained or gas pressure supplied at timed intervals as by means ofcontrol valve 32 mounted in line 30 between passageway 28 and the gassupply source.

Multi-section mold 18 having mold sections 18a and 18b is provided toform a cavity generally designated 20 in which to blow mold and shape anarticle. Extrusion head 12 is so disposed that mold 18 may be broughtinto registry therewith.

In the illustrated embodiments, mold sections 18a and 1812 arepreferably mounted on a conventional rotary turret table not shown whichpreferably carries a plurality of equally spaced molds not shown,identical with mold 18. As is hereinafter described in greater detail,operation of mold 18 may be automatically controlled in time sequencewith the operation of extrusion head 12 and other components of theapparatus by suitable timing mechanisms not shown.

Referring now to the parison cutting and sealing apparatus which is aspecial feature of the present invention as illustrated in FIG. 4, thereis provided a piston operated scissors like assembly 34. Piston 36 isconnected to rod 38 within housing 39. Toggle joint 41 comprises cutterpivot member 40 and sealer pivot member 42, and rod extension 46, allthree being pivotably mounted together ondtgggle pin 44, with rodextension 46 rigidly joined to ro Pivot member 40 has one end pivotablyconnected at 48 to cutter blade support member 50. Sealer pivot member42 is likewise pivotably connected at one end at 52 to sealer bladesupport member 54. Sealer blade 56 is joined, for example, byconventional bolting to sealer blade support member 54 at 58. Cutterblade 60 is likewise conventionally bolted at 62 to cutter blade supportmember 50. Adjustable cutter blade eccentric bushing 64 is provided topermit varying the amount of travel of the cutter blade in relation tothe sealer blade. That is, the amount of open space between blades 56and 60 may be varied from that shown in FIG. by means of adjustableeccentric bushing 64. This adjustment is desirable to compensate for thevarying parison wall thicknesses and diameters encountered. Sealer bladebushing 66 is mounted in sealer blade support member 54 and may also bean adjustable eccentric, though ordinarily only one is required perassembly. Mounting of the adjustable eccentric may be either'on thecutter or sealer blade assembly. Bushings 64 and 66 also represent thepivot points about which the cutter and sealer support members rotatewhen piston 36 is activated. Though desirable, the adjustable eccentricfeature of the bushing may be eliminated and any means provided topermit pivoting support members 50 and 54; a bearing or pivot pin forexample may be utilized. Likewise the pivot means may be mounted in theblades and the support members eliminated desired.

In FIGS. 1 and 2 are shown schematically the cooperative relationshipbetween sealer blade 56 and cutter blade Cutter blade 60 has step 62extending along its length, with cutting edge 64 extending along theouter end of the horizontal portion of step 62. Tapered surface 66recedes downwardly and inwardly from edge 64. The thickness of sealerblade 56 should generally be equivalent to the height of the verticalportion of step 62. Both cutter blade 60 and sealer blade 56 must belaterally alignable to permit sealer blade 56 to fit within step 62 toprovide cutting line when the blades are in the closed position depictedin FIG. 2. The location of the step and the tapered surface may bereversed however, with the step situated below the tapered surface andthe sealer blade accordingly mounted laterally opposite it.

Blow assembly 68 is shown in FIG. 3, which comprises blow head 70 andblow head assembly arm 72. Channel 74 is provided in blow assembly 68and is connected to a pressurized gas supply source, not shown.

The sequence of operations of this embodiment of the invention istypically as follows: As shown in FIG. 1, hot thermoplastic materialissuing from reservoir 15 of extrusion head 12 is extruded throughannular outlet orifice 14 to begin to form a generally tubular length ofthe material. Mold halves 18a and 18b are in the open position inregistry with extrusion head 12. Cutter and sealer blades 56 and 60 arelikewise in open position, after having previously cooperatively closedto sever the previous unit and seal the open end of the next succeedingparison, the sealed end shown at 78 in FIG. 1. During extrusion of theparison, and preferably after /2 to of the length of the parisonnecessary to form an article has been extruded, control valve 32 isopened to permit introduction of low pressure, putt gas throughpassageway 28 in inner core 22 into the tubular length being formed, topartially expand the tubular length into bulblike shape 76. Afterformation of partially expanded bulblike shape 76, mold halves 18a and18b are closed around it as shown in FIG. 2, with tail 78, which wasformed when the previously extruded bulb-like shape was cut and sealed,being pinched in the usual manner at the bottom between cooperatingedges of the mold halves. Simultaneous with the closing of the moldhalves or immediately thereafter, the cutter and sealer blades areclosed and extrusion head 12 is removed from alignment with mold 18 withblow head assembly 68 then brought into alignment therewith closing ofthe cutter and sealer blades is accomplished when piston 36, piston rod38 and rod extention 46 of scissors like assembly 34, shown in FIG. 4,are moved to the right under the influence of a suitably suppliedconventional pressurized fluid so that rod extension 46 is in theposition shown in outline form in FIG. 4. As rod 38 moves to the right,members 40 and 42 pivot about toggle pin 44 at one end and about pivotpoints 48 and 52 at their other ends, with the latter ends movingoutwardly, while support members 50 and 54 privotally connected tomembers 40 and 42 at 48 and 52, also pivot about bushings 64 and 66 as aresult of this movement of rod 38. The ends of support members 50 and 54at 58 and 62 thereby move inwardly to cooperatively move cutter blade 60and sealing blade 56 into closed position as shown in FIG. 2, and inphantom outline in FIG. 4, thereby simultaneously severing the partiallyexpanded bulb-like shape and sealing the bottom end of the nextsucceeding one. After remaining in the closed position momentarily, thedirection of movement of the piston 36 is reversed by conventionalmanipulation of the pressurized fluid flows, and the blades return tothe position depicted in FIG. 4 as another extrusion cycle commences,

Further expansion or blow molding of the partially expanded bulb-likeshape into the finished article is performed after the mold is removedor as it is being removed from alignment with extrusion head 12, bydirecting pressurized fiuid through channel 74 of blowhead assembly 68as illustrated schematically in FIG. 3. After the article is formed, themold may be opened after which the formed article may be removed orblown from the apparatus in the usual manner, and the waste tail at thebottom and sprue at the top of the article trimmed off by conventionalmeans.

As can be appreciated from FIG. 2 the top of partially expandedbulb-like shape 76 is kept open during the severing operation due to theinfluence of tapered surface 66 of cutter blade 60. Maintaining the topof the enclosed bulb-like shape open permits escape of preinflation airand keeps the end of the bulb-like shape in a belled out position topermit the end of the blowhead assembly to enter.

-In FIGS. 5 and 6 is schematically depicted an alternate embodiment ofthe cutting and sealing apparatus of the present invention whichfeatures parison gripping provisions. Cutter blade 80 and sealer blade82 are constructed similarly to those previously described except thateach here has an upwardly and outwardly tapering sealing surfacedepicted respectively at 84 and 86.

Cutter blade 80 is provided with 2 identical gripping assemblies 85a and8512, as shown in FIGS. 5 and 6, only one of which will here bedescribed in detail. Gripping assembly 85a comprises sleeve or channelmember 88 which is joined to cutter blade 80. Channel member 88 haschannel 90 therein, within which movable jaw 92 may move horizontiallyback and forth. Stop member 94 is connected to channel member 88 byconventional means, for example by bolt 96. Biasing means are providedby compression spring 98 which is connected at one end to stop member 94and at the other end to movable jaw 92 and is under compression when thecutter and sealer blades are in open position so as to urge movable jaw92 away from stop member 94. Sealer blade 82 has fixed jaws 100a and100b attached thereto by conventional means, for example, by bolt 102.Conventional means (now shown) must be provided for limiting the maximumoutward movement away from stop member 94 of jaw 92 in channel member88. For example, a slot may be bored in jaw 92 in which rides a pinrigidly connected to channel member 88. The pin and slot arrangementwould prevent spring 98 from urging jaw 92 completely out of channel 90when the blades are in open position. Cutter and sealer blades 80 and82, gripping assemblies 85a and 85b and fixed jaws 100a and 10% aretoggle mounted and fluid operated in a manner identical with thatpreviously described and depicted in FIG. 4.

When the process is operated with the apparatus depicted in FIGS. 5 and6, after partially expanded bulblike shape 104 has been inflated, cutterblade 80 and sealer blade 82 cooperatively close to sever bulb-likeshape 104 and seal the end of the subsequent blank as depicted in FIG.5. On closing, movable jaw 92 abuts against fixed jaw 100a and in sodoing squeezes, flattens, and grips a portion of the bulb-like shape asshown typically at 106 in FIG. 6. The top 108 of bulb-like shape 104remains open, however, because of the influence of downwardly taperingcutting surface 87 of cutter blade 80. While the bulb-like shape isgripped and supported in two places between gripping assemblies 85a and85b and jaws 100a and 100b, and with top 108 open to the atmosphere,some pre-inflation air escapes and the partially expanded bulb-likeshape relaxes and flattens out somewhat, before the mold halves areclosed about it. After closing of the mold, the blowhead assembly isconventionally moved into alignment therewith and the relaxed, stretchedbulb-like shape further expanded to the final article configuration. Themold halves are then opened and the article removed, and the tail at thebottom and sprue at the top of the article as well as the flash materialformed by the squeezing action of the jaws at the upper end of thepartially expanded bulb-like shape are trimmed off by conventionalmeans. The upward and outward taper of sealing surfaces 84 and 86facilitate removal of the sealed end of the subsequent bulb-like shapefrom 6 that being cut when extrusion head 12 is vertically lifted, forexample, away from the area where the seal was formed.

In this embodiment, when cutter blade and sealer blade 82 are in closedposition without squeezed plastic therebetween, movable jaws typicallyshown at 92 and fixed jaws a and 10% are initially set by means of aneccentric bushing previously described and shown at 64 in FIG. 5, sothat their opposing end faces are in touching contact. The horizontalmovement of the movable jaws permitted by means of springs 98,thereafter permits griping different thicknesses of plastic between thefixed and movable jaws without need for adjusting the travel of blades80 and 82 on each occasion.

Use of the gripping provisions of FIGS. 5 and 6 also permit supportingthe bulb-like shape while it is being transported to a waiting mold, orwhile the mold halves move in on it as it hangs below the extrusionhead. It should be understood that the movable gripping jaws depicted inthis form of the invention, may, if desired, alternatively be mounted onthe sealer blade with the rigid jaws mounted on the cutter blade.Ordinarily it makes no difference on which blade the movable jaws aremounted.

FIGS. 7, 8 and 9 illustrate still another modification of the techniquefor cutting and sealing a pre-inflated parison as herebefore described.In this embodiment cutting and sealing are performed by separate means,rather than by the same apparatus as depicted in FIGS. 1 and 2.Extrusion tip 113 of cylindrical inner core of extrusion head 112 has afrusto-conical tapered portion 114 near its lower end, having an outersurface 116. Cylindrical end portion 118 of extrusion tip 113 isconnected to tapered portion 114 at the lowermost extremity of taperedportion 114, and cooperates with shoulder 120' of extrusion ring 121 todefine annular extrusion outlet orifice 122 in extrusion head 112, wheninner core 116 is in an upper extruding position as depicted in FIG. 8.Reservoir is provided within extrusion head 112. Inner core 110 haschannel 111 which may be connected to a pressurized gas source (notshown) as mentioned previously. In this embodiment, the cutter bladedepicted previously is eliminated and replaced by a second sealer bladeidentical in construction to that previously described. Therefore,primary and secondary sealer blades 124 and 126 are provided withactivating means identical to that portrayed in FIG. 4.

In the operation of this alternate embodiment, the parison is expandedinto partially expanded bulb-like shape 128 by low pressure gas enteringthrough channel 111 as previously mentioned while mold halves 18a and18b are in open position surrounding bulb-like shape 128, sealer blades124 and 126 are in spaced apart, open relationship and inner core 116 isin its upper extruding position, which position is depicted in FIG. 8.As previously stated, pre-inflation commences when about /2 to of thelength of parison necessary for formation of the article has beenextruded. After partially expanded bulblike shape 128 has been formed,the flow of pressurized gas is interrupted by closing a suitable valvein the pressurized gas supply line to channel 111 (not shown but similarto 32 in FIG. 1) and inner core 110 is moved axially downward so thatoutside surface 116 of frustoconical tapered portion 114 momentarilycompresses the extruding parison against shoulder of extrusion ring 121as shown in FIG. 7, so as to score and thin out the wall of thepre-inflated parison at this upper end point. Inner core 116 isthereupon moved axially upward to its previous extruding position asdepicted in FIG. 8. During this momentary compression of the upper end,there is a corresponding momentary interruption in the flow of hotthermoplastic in the flow channel of reservoir 115. Simultaneous with orincrementally in time after the scoring of the end of partially expandedbulb-like shape 128, mold halves 18a and 18b are caused to close aroundthe bulblike shape 128, and extrusion head 112 is lifted axially upwardand away from the mold 18, while plastic continues to issue from theextrusion outlet orifice in a generally tubular form. With this movementof the extrusion head and mold, the scored end of the pre-ini'latedbulb-like shape is held by mold halves 18a and 18b, and sufficientlystretched by the lifting head at the point where it is scored, so thatit is torn or pulled apart from the end of the subsequent blank asdepicted in FIG. 8. As extrusion head 112 begins to move axially upward,cooperating sealer blades 124 and 126 close as shown in FIG. 9 to sealthe bottom of the continuously extruding tube from which the nextbulb-like shape will be formed, and mold 18 is moved out of verticalalignment with extrusion head 112 while another mold moves into verticalalignment therewith, the outline of which is partially shown as 131 inFIG. 9. When the bottom end is sealed, the pre-inflation gas shutoffvalve is opened at the proper time during extrusion of the next parison,to commence another cycle and extrusion head 112 is lowered between thehalves of the subsequent mold (131) while the next bulb-like shape isbeing formed.

After bulb-like shape 128 has been enclosed 'Within the cooperating moldhalves with sealed bottom portion 130 gripped at the bottom of the moldbetween cooperating projections, or simultaneous with the closing, aconventional blowhead assembly is moved into alignment with the mold andthe bulb-like shape further expanded into the final articleconfiguration as described previously and typically illustrated in FIG.3.

As an alternate to the sealing of the parison end on the upward lift ofthe extrusion head in the embodiment of FIGS. 7-9, sealing may beaccomplished on the downward stroke prior to pre-inflation, but withthis procedure the hot thermoplastic has a tendency to build up on thesealer blades.

Conventional apparatus, for example, pressurized air or hydraulicallyoperated piston means or cam drive means cooperating with an upwardlythrusting spring (not shown) may be employed to axially move inner core110. Similar conventional piston means may be utilized to open and closethe mold halves.

The above description and particularly the drawings are set forth forpurposes of illustration only and are in no way to be taken in a limitedsense.

As previously mentioned, this invention is directed toward a method andapparatus for forming hollow plastic articles having neck and bodyportions, comprising the steps of extruding moldable plastic materialfrom a supply source downwardly through an outlet orifice to form agenerally tubular length of the material, clamping the tubular lengthbelow the outlet orifice to form a seal across the tubular length,injecting gas into the portion of the length above the seal to partiallyexpand said portion, enclosing the partially expanded shape within apartible mold having adjacent neck and body forming cavities, andfurther expanding the partially expanded shape to form the hollowarticle.

It is essential with the method and apparatus of the present inventionthat the parison be extruded in a downward direction whereby it may bepartially expanded while suspended below the extrusion nozzle under theinfluence of its own weight, and without the need for separate endsupport.

It will be understood that the means for supplying a timed flow of gasthrough the passageway in the mandrel is merely illustrative and that awide variety of alternatives may be employed to properly time andcoordinate the gas thus supplied with the several operations of theplastic blowing and extruding apparatus.

It will be appreciated that although the present invention empolysmovement of the extrusion nozzle and blowhead assembly for alignment ofthese elements with the mold, the present invention includes theconverse movement within its scope, i.e., movement of the mold to alignit with the extrusion nozzle and blowhead assembly.

The cutter and sealer blades and their supports mounted on apneumatically operated toggle joint may be designed to close and open ona single stroke of the piston by providing a piston having a stroketwice the length of that previously described. In a process notrequiring pre-infiation wherein the parison end need not be sealed, thesealer blade may be replaced with a cooperating cutter blade. Thoughpneumatic operation is preferred, other types of moving or activatingmechanisms may be employed to operate the cutter and sealer blades.

Utilization of gripping jaws in conjunction with the cutter and sealerblades is particularly advantageous in the present invention since itpermits escape of some of the pre-inflation gas through the open top endof the partially expanded bulb-like shape prior to enclosing it withinthe mold, thereby relaxing the bulb-like shay: somewhat. In doing so,however, the bulb-like shape is not returned to a tubular form butremains in a thinnedout partially expanded state. Discharge of some ofthe pro-inflation gas from the bulb-like shape prior to blowingdecreases the possibility of formation of chill marks in the finishedarticle. These are rough areas formed on the outside surface of thepre-inflated parison when the pre-infiated parison touches the cooledwalls of the mold cavity on closing the mold. The plastic in these areassets up so as to prevent further expansion during final blowing. Thoughit is not essential that the pre-inflation gas be partially vented priorto final blowing, it is preferable that some of the gas be discharged.

Though the extrusion head may be stationarily mounted, it is preferredin the present invention that it be movably mounted as, for example,mounting for vertical movement as disclosed in US. Pat. No. 2,349,186.With this mounting method, after the pre-inflated parison is enclosedwithin the mold, the extrusion head is caused to bob upward a shortdistance while the parison and/ or bulb-like shape for the next articlecontinues to extrude out the orifice. A revolvable rotary turret tablecontaining a plurality of molds may be provided to index the loaded moldto one side and position an adjacent open empty mold into the positionoccupied by the previous one. The extrusion head is then caused to bobdown as the subsequent bulb-like shape is being finally formed so as toposition it within the subsequent empty mold. This extrusion iscontinuous and is maintained at a rate approximately equal to thevelocity of the extrusion head as it bobs up and down. Through extrusionhead lift is the preferred method, the system could also operate byutilizing the parison jaw gripping arrangement previously described totransport a pro-inflated parison either axially or horizontally to amovable mold from a stationary extrusion head at a rate faster than theparison is being extruded.

Any plastic material capable of being blown may be utilized in thepresent invention. Typical materials are thermoplastics such as low orhigh density polyethylene, polypropylene, polymers of vinyl chloride orpolystyrene. As the density and toughness of the material increases, theamount of stretch achievable increases. Unusually good results areobtained therefore with high density polyethylene which is such atypical and preferred material. Polyvinyl chloride is also of similarconsistency.

The resiliency, temperature and thickness of the plastic being extrudedwill determine the pressure of the pre-infiation gas required in thepresent invention. For most materials this pressure should be maintainedbetween about /3 to about 5 p.s.i. above atmospheric pressure at the endof the inner core or mandrel of the extrusion head, and the temperatureof the gas between about 20 F. to about F. At temperatures below about20 F., cold spots may occur in the inner parison surface with the resultthat pre-infiation of the parison may be non-uniform. In the case ofhigh density polyethylene the pressure should be between the limits ofabout A to about 3 p.s.i. above atmospheric pressure, and the gastemperature between about 50 F. to about 100 F., for unexpanded parisonwall thicknesses between about & in. to about A in. and parisontemperatures between about 380 F. to about 460 F. At pressures less thanA; p.s.i. no appreciable expansion is realized. At pressures greaterthan about 5 p.s.i. expansion is excessive and results in theundesirable, unexpandable chill or rough spots in the finished articlepreviously mentioned. Also at such high pressures excessive flash isformed along the parting line of the mold halves and bursting may evenoccur. Preinflation pressure determines the amount of radical expansionof the parison to be attained and may be varied with the material beingextruded and the extrusion temperature to control the size of thebulb-like shape so that it just touches or is slightly smaller inmaximum width than the minimum projection within the mold, therebyeliminating or minimizing chill marks.

It should be understood that with the axially movable mandrel embodimentof the present invention, the parison may be either severed completely,or scored so that the parison wall thickness is reduced such that aminimum pull by either a moving extrusion head or mold tears thebulb-like shape from the end of the next succeeding parison. As thetapered lower portion of the mandrel wears with use due to its severingor scoring action, it may be replaced if designed to be removablyconnected to the bottom of the mandrel. Use of this embodiment separatesthe cutting and sealing functions of the blades thereby decreasingmechanical wear and optimizing the action of each.

With the process of the present invention, it should be noted thatsubstantially no axial stretching of the parison occurs during thepre-infiation step but rather a generally radial expansion takes place.The time during which the pre-infiation air is on during extrusion alsodetermines the degree of radial expansion. In the present invention thismay vary between and 100% of the time to extrude the length of parisonrequired to form one article.

Furthermore, the complete article including the neck is molded in asingle step from the pre-inflated parison. Extrusion preferably iscontinuous rather than intermittent. Recirculation of the extrudingmaterial during mold changes is thereby eliminated.

The principal advantage of the method and apparatus of the presentinvention is the production of economical light weight non-cylindricalor irregularly shaped bottles having extremely uniform body walldistribution, while utilizing the same quantity of plastic material asin forming a cylindrical body. Distribution is improved since expansionis more uniform by use of a pre-inflated parison, that is, the distancebetween the wall of the mold cavity and the outside surface of thebulb-like shape prior to final expansion is more constant.

With the pre-infiation or puif blow step of the present invention, theparison is expanded to a larger diameter than that which it has onissuing from the extrusion nozzle, and in so doing is thinned outuniformly. A smaller tubing may thus be extruded to provide the sameweight of plastic in the finished article. The extrusion ring and tipmay be reduced in size in blowing a large diameter article rather thanincreased as is necessary without use of the pre-inflation step.Utilization of a reduced orifice reduces the extruder discharge headpressure necessary to force the plastic through the orifice.Furthermore, a single extrusion ring and tip may be used in formingvarious different sized containers merely by varying the time thepre-infiation gas is kept on and the pressure thereof.

Use of a reduced diameter parison also minimizes flash formation in thetail pinch area due to its undersized character.

The surface characteristics of the extruded parison 10 prior topre-inflation may be varied according to the method and apparatusdisclosed in copending application Ser. No. 391,920, filed Aug. 25, 1964and now abandoned, assigned to Monsanto Company.

The scissors assembly of the present invention comprising the cutter andsealer blades or the dual sealer blades may be independently mountedbetween the extrusion head and mold(s) or may be connected eitherpermanently or removably to the extrusion head itself.

The method and apparatus of the present invention is applicable informing any article having neck and body portions, and is especiallyapplicable to non-cylindrical irregularly shaped bodies where it isnecessary to blow one side further than the other, e.g., those withoval, rectangular or oblong cross sections. It is particularly adaptablein forming handleware bottles and most especially for handleware bottleshaving non-cylindrical elongated cross sections.

Various other modifications and alterations will be readily suggested topersons skilled in the art. It is intended, therefore, that theforegoing be considered as exemplary only, and that the scope of theinvention be ascertained from the following claim:

What is claimed is:

1. A method of forming a hollow article of moldable plastic materialcomprising the steps of:

(a) extruding moldable plastic material from a supply source through anannular outlet orifice to form a generally tubular length of thematerial;

(b) clamping the length axially below the outlet orifice to form a sealacross the tubular length;

(0) injecting gas into the portion of the length above the seal topartially expand said portion into a bulblike shape;

(d) severing the bulb-like shape from the generally tubular length atthe end of the bulb-like shape closest to the outlet orifice to form anopen severed end separated from the length;

(e) advancing each of two movable jaws toward oppositely positionedstationary members with the upper end portion of the bulb-like shapeinterposed there between to grip the open, severed end of the bulblikeshape simultaneously with severing while maintaining the severed endopen, thereby supporting the bulb-like shape in two flash defining areasthereof;

(f) releasing the previously injected gas from within the bulb-likeshape through said open end to cause said bulb-like shape to contract insize;

g) enclosing the contracted bulb-like shape within a partible moldhaving a cavity conforming to the shape of the article;

(h) expanding the contracted bulb-like shape within the partible mold toform the hollow article; and

(i) separating said fiash from said formed article.

References Cited UNITED STATES PATENTS 3,339,232 9/1967 Battenfeld etal. l85(BZ) 3,362,043 1/1968 Langdon et a1 26494X 3,399,424 9/1968Sheptak 26494X 3,425,090 2/1969' Nave et al. 26498X 3,343,210 9/1967Guignard 26498X 3,479,421 11/1969 Armbruster et al. 264-98X FOREIGNPATENTS 1,450,395 7/1966 France 264-98 ROBERT F. WHITE, Primary ExaminerT. J. CARVIS, Assistant Examiner

